Multicarrier Spectral Shaping Performance in Non-White Interference Channels: Experimental Results

In a recent work, we proposed a spectral shaping (SS) algorithm, which via adaptively selecting and allocating subcarrier powers at the transmitter can attain additive white Gaussian noise (AWGN) theoretical performance results in non-white (e.g., interference) spectra. This algorithm, knowing the received interference channel power spectral density at the transmitter, solves an optimization problem to maximize the Shannon capacity subject to a few constraints. Solving this problem provides the selected subcarriers and allocates the total available power among them in order to attain the equivalent AWGN channel bit error ratio (BER), hence improving performance and maximizing the reliability, which is critical for aeronautical communication systems. One simple idea for point-to-multipoint communication using SS is that subcarriers experiencing very high interference are not used for the specific air-station (AS) which is experiencing the high-power interference, but they can still be used for other users. In this paper, after a brief description of the algorithm, via measurements, we test the algorithm and show the measurement results. The spectrally non-white channel can be from non-white noise, or more commonly, interference. In these measurements, the SS communication system was tested along with the Gaussian pulse shaped distance measuring equipment (DME) signals. The DME is pertinent for currently proposed L-band aviation communication systems, where an orthogonal frequency division multiplexing (OFDM) based system, the L-band digital aeronautical communication system (LDACS) has been proposed as an inlay multicarrier communication system between the DME channels. The results presented in this paper using 64-QAM modulation order as a highly required energy-per-bit modulation example, show how using this adaptive technique can improve performance and reliability especially in low SNR situations, hence could be beneficial for future applications in L-band aviation or other non-white channels in other fields.